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| Front | oxygen concentration change |
| Back | a large decrease in oxygen concentration stimulates the peripheral chemoreceptors, and nerve impulses are transmitted to the respiratory centre nerve impulses stimulate the transmission of messages to the diaphragm and intercostal muscles, so breathing rate and depth increases |
| Front | steps of fossilisation |
| Back | The organism dies, and its remains are left in an environment conducive to fossilisation (e.g. near water or in sedimentary layers) soft tissues decompose, leaving only hard parts like bones, teeth or shells the remains are rapidly buried by sediment, such as sand, mud, or volcanic ash, which protects them from scavengers, weathering or decay over time, minerals in groundwater infiltrate the remains, replacing the organic material and turning them into rock-like structures (petrifications) layers of sediment accumulate, and the pressure compresses the remains sediments harden into rock, encasing the fossil Geological processes (e.g. tectonic activity or erosion) expose the fossilised remains to the Earth’s surface where they can be discovered |
| Front | dendritic cells |
| Back | deliver the ‘marching orders’ to the rest of the immune system agents which tell those agents what to attack located in areas that are vulnerable to infection, actively surveying their local environment for signs of pathogens and damage to the body’s own cells use their highly mobile and elongated arms to scan various particles near them, known as antigens, which are produced by pathogens after consuming these antigen particles, the dendritic cells break them down into smaller components, which are displayed on the cells surface to broadcast the contents of their recent meals detect, engulf and process foreign particles |